<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
    function fun(n){
        if(n == 1){
            return 1;
        }
        return n * fun(n - 1);
    }
    var ret = fun(5);
    console.log(ret);
    </script>
</head>
<body>
    
</body>
</html>